The invention relates to a method and a system for monitoring of the functionality of an injector. In particular, the method and the system relates to the monitoring of an After Treatment Injector (ATI) for injection of a fluid in an engine exhaust gas system. The monitoring is performed by using a pressure sensor which detects the pressure of the fluid delivered to the injector for a specific condition or injection cycle whereby the pressure or pressure fluctuations may be registered and compared with reference values in order to indicate the state of the injector. The invention is suitable to be used as a part of the On Board Diagnosis (OBD) system.
In vehicles today, the feature of being able to monitor, regulate and control an exhaust gas purification system comprising a filter and/or catalyst is of major interest in order to provide a well functioning exhaust gas treatment system. One suggestion to improve the functioning and control of such a treatment system, in particular those systems used for heavy duty vehicles operated by a diesel internal engine, is to include a separate injector in the exhaust gas system downstream of the engine exhaust gas outlet and upstream of at least one of the purifying devices, e.g. a filter, NOx trap or catalyst, in order to inject a liquid for enhancing the performance of the system. The injected liquid may for example be urea, which is used to improve the efficiency concerning NOx reduction, or hydrocarbons, which may be added to be combusted and thus increase the temperature of the gases in order to regenerate the filter.
In the case an exhaust gas purification system comprises such an injector as described above, commonly named After Treatment Injector (ATI), the performance of the system is highly dependent on the functioning of the injector device. If the liquid not is injected properly in the exhaust gas stream there will be negative environmental consequences due to malfunctioning of the purification system.
One known way of indicating the functioning of the system may be to measure the exhaust gases which pass the purification device. In case of NOx reduction, the NOx content after the treating unit may be calculated or measured by a lambda sensor which indicates the level of NOx coming out of the system. From the measured or calculated levels of NOx it is possible to conclude the functionality of the exhaust gas purification system. In the case of addition of hydrocarbons or some kind of fuel in order to elevate the temperature, either the temperature or the content of fuel in the exhaust gases passing the purification system may be measured or calculated in order to determine whether the system is working satisfactorily or not. However, these systems have the drawback of not unambiguously pointing out what part of the purification system that is not working in a sufficient way, e.g. it may be that the NOx trap, the filter and/or the catalyst is deteriorated and not working efficiently enough or it may be the ATI which is malfunctioning. Hence, it is not possible to indicate which part that should be investigated or changed in order to make the system work satisfactorily again.
In EP 1 176 292, a system is disclosed for monitoring of the functionality of an ATI (After Treatment Injector). This system includes an exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine, a reducing-agent supplying mechanism for supplying a reducing-agent to the exhaust gas passage upstream of the catalyst and pressure detecting means for detecting a pressure in the reducing-agent supplying mechanism. The reducing-agent supplying mechanism comprises an injection nozzle arranged in an exhaust passage, a reducing-agent supplying passage for conducting reducing-agent to the injection nozzle, an amount controlling valve for controlling an amount of reducing-agent injected by the injection nozzle and a shut-off valve for shutting off the reducing-agent supplying passage.
On the basis of the pressure detected by the pressure detecting means, abnormality of the reducing-agent supplying mechanism is detected by an abnormality determining means. By this system it may for example be possible to detect when reducing-agent is leaked from the reducing-agent supplying mechanism or to detect if reducing agent is leaked out of or into a closed space defined in the reducing-agent supplying mechanism, e.g. when a passage from the shut-off unit to the reducing-agent adding unit is closed. Furthermore, if the reducing-agent adding unit is clogged, it may be detected by the pressure sensing unit that the pressure downstream from the passage opening/closing valve becomes difficult to be lowered after the valve opening period. If the reducing-agent adding unit is brought into a failure in closing, the pressure downstream from the passage opening/closing valve becomes lower. Further, when the passage opening/closing valve is brought into a failure in opening or closing the valve, the passage opening/closing valve is always closed/opened and therefore, the pressure downstream from the passage opening/closing valve becomes constant during the valve opening period and before and after the valve opening period.
Hence, when an abnormality is caused in the reducing-agent adding unit and/or the passage opening/closing valve, the pressure downstream from the passage opening/closing valve during, before or after the valve opening period of the passage opening/closing valve, indicates a value in accordance with the characteristic of the abnormality. Therefore, the abnormality determining means can determine abnormality of the reducing-agent adding unit and/or the passage opening/closing valve on the basis of pressure detected by the pressure detecting means during, before or after the valve opening period of the passage opening/closing valve.
In DE 10 2005 001 119 it is disclosed a method for operating an internal combustion engine. III said patent application it is disclosed a method for analysing the functionality of the pressure sensor, flow regulator and fuel injector by providing a particular scheme of opening and closing of said fuel injector and flow regulator.
However, the system described in EP 1 176 292 does not provide a solution for how an injection system can be systematically checked for its functionality and providing a self-testing function in order to monitor the condition of the reducing-agent supplying mechanism and how to adapt the system for irregularities for individual components and systems, e.g. due to differences at manufacturing, at upgrading of the system or due to deterioration of system components. In addition, the above described system does not provide a solution for checking the pressure sensor itself and may therefore indicate a fault of the valves or injector if the sensor not is working.
Hence, there is still a need to provide an improved method which provides robustness in checking the functionality of an After Treatment injector (ATI).
A system for performing the method according to an aspect of the present invention comprises an After Treatment Substance Injection System (ATSIS) including an After Treatment Injector (ATI). The ATI is located in an engine exhaust system downstream an outlet for exhaust gases from combustion chambers of an engine, e.g. a diesel IC-engine. The ATI is further located upstream of a purification unit in the exhaust gas system, e.g. a filter, catalyst or trap, so as to inject a substance in the exhaust gases in order to enhance a functionality of the system, e.g. the adding of urea to improve the NOx-purification of the exhaust gases or to add HC-containing substance (fuel) for the purpose of regeneration of a filter unit.
As will be evident from the following, it is not necessary to specify the substance to be injected into the exhaust gas stream but the inventive system will work for adding of a desired substance. In some aspects, it will improve the monitoring efficiency if the system cooperates with another On Board Diagnosing (OBD) system which is able to detect the overall functionality of after treatment exhaust gas system.
The ATI is connected to a supply tank of the desired substance to be injected to exhaust gas treatment system, e.g. to the fuel tank of the vehicle, a separate fuel tank or to a urea or ammonia tank, by a conduit.
The After Treatment Substance Injection System (ATSIS) further comprises a flow control unit for controlling the pressure in the conduit for supplying of the substance from the container to the After Treatment Injector (ATI). The flow control unit may for example be a valve arrangement which may be closed, to cut off the connection to a pressurized system upstream the valve, or open, to set the pressure downstream the valve to the same as upstream, e.g. to the same value as a pressurized tank. As another alternative the flow control unit may be a pump or compressor which may pressurize the system downstream of said pump or compressor.
A pressure sensor is located downstream of said flow control unit in the ATSIS so as to be able to measure the pressure of the substance which is to be injected from the ATI into the exhaust gas stream.
The ATSIS also comprises an Electronic Control Unit (ECU) which is controlling the opening and closing of the flow control unit and the After Treatment Injector (ATI).
In order to monitoring the system performance of the ATSIS, an On Board Diagnosing (OBD) system is connected to the ECU and the pressure sensor. The OBD is provided with comparative data for the functionality of the After Treatment Substance Injection System (ATSIS) in order to detect abnormal functionality of the ATSIS.
The system may of course be monitored continuously by the pressure sensor during normal drive of a vehicle comprising the above described system. However, it is not sure that the normal monitoring function will be sufficient to detect some abnormal activities or it may also be possible that the system indicates an error when the system is performing as it should, e.g. when there is a malfunctioning of the pressure sensor. By the use of a specific, predefined sequence of opening and closing commands for the flow control unit and the After Treatment Injector (ATI) for the sole purpose of monitoring the functionality of the system, a more accurate and reliable measurement of the system will be achieved. It will thus be easier to detect malfunctioning of the ATSIS at an earlier stage and also to better locate the cause of the malfunctioning of the ATSIS. Hence, the ECU may be programmed to send out control signals to the flow control unit and the ATI to close and open following a specific sequence and timing for changing their positions. During such a monitoring cycle, the output values from the pressure sensor are logged such that the actual pressure data may be compared with the comparative data in the OBD system. According to specific criteria for indicating a malfunction of the ATSIS (e.g. a certain pressure value outside the allowed range or a change of a pressure value being outside the allowed limit), it may be possible to deduce which part, e.g. the flow control unit, the After Treatment Injector (ATI) and the pressure sensor, which is malfunctioning and in which way it is deficient.
The control sequence may for example be performed at certain time intervals, on demand of a driver or as a consequence of a fault detected in the exhaust gas treatment system by an On Board Diagnosing (OBD) system. There may also be several different control sequences programmed in the ECU which differs in the consecutive order of performing the opening and closing commands and in the time intervals for the changes of the status of the controlled devices (the ATI and the flow control unit) from open to closed. For example, when it is desired to monitor if there is a small leak in the system, it might be desired to keep the controlled devices in a fixed state so as to be able to detect a slow change in the pressure.
According to an embodiment of the invention, the control sequence to be performed is as follows:    1. Set the flow control unit to open and set the ATI to closed.    2. Close the flow control unit and keep the ATI closed.    3. Keep the flow control unit closed and open the ATI    4. Keep the flow control unit closed and close the ATI.    5. Open the flow control unit to open and keep the ATI closed.
The time duration that each sequential step keep the ATI may be adjusted to best fit the purpose of what feature that is to be detected. However, in order to perform data which is comparable with the reference data in the OBD system the sequential monitoring should be performed according to any of these reference sequential timings.
In table 1 below it is described the output from the pressure sensor depending on different possible faults of a number of relatively frequently occurring faults when using the above described control sequence. In this system it is suggested that the flow control unit comprises a regulating valve which may be closed or opened in order to allow flow of the desired substance from a pressurized supply through a conduit to the ATI. The pressurized supply and the valve may of course be substituted for a pump or the like which also may be detected according to the table below. In that case “Valve closed” corresponds to non-functioning of the pump, “Valve clogged” to reduced pumping effect of the pump, “valve leakage” to a continuous, low pumping action of the pump and “Valve open” to a continuous high pumping effect of the pump.
TABLE 1Functionality12345All functionsSystemSystemNormalLowNormalOKpressurepressurepressurepressurepressure risedrop curvecurveATI closedSystemSystemSystemSystemSystempressurepressurepressurepressurepressureATI cloggedSystemSystemSlowLowNormalpressurepressurepressurepressurepressure risedrop curvecurveATI leakageSystemPressureReaches fastLowSlowpressuredroplow pressurepressurepressure risecurveATI openSystemFastLowLowLowpressure orpressurepressurepressurepressure,lowerdrop to low(maybe apressure *pressurelittle riseValve closedLowLowLowLowLowpressurepressurepressurepressurepressure(could be(could be(could besystemsystemnormalpressure ifpressure ifpressurethe conduitthe conduitdrop curve)is full)is full)ValveSystemSystemNormalLowSlowcloggedpressurepressurepressurepressurepressure risedrop curvecurveValveSystemSystemSlowIncreasedReaches fastleakagepressurepressurepressurepressuresystemdrop curvepressureValve openSystemSystemSystemSystemSystempressurepressurepressure orpressure orpressureextra slowfastpressureincreaseddrop curve *pressure tosystempressureSensor HighSystemSystemSystemSystemSystempressurepressurepressurepressurepressureSensorMiddleMiddleMiddleMiddleMiddlemiddlepressurepressurepressurepressurepressureSensor lowMiddleMiddleMiddleMiddleMiddlepressurepressurepressurepressurepressure* = The different responses are dependant on flow ratio between valve and ATI (e.g. if the valve is open and allowing a larger flow than the ATI, the valve will fill up the system fast and keep the pressure constant also when the ATI is open).
By following a programmed sequence of opening and closing commands for the flow control unit and the (ATI) it will be possible to distinguish faults of different components which not may be distinguished by one single measurement or by only measuring the absolute values of the pressure in different conditions. For example, the occurrence of a slow pressure drop curve in step 3 (The valve is kept closed and the ATI is opened) indicates either valve leakage or ATI clogged. However, these faults may be distinguished in step 4 (The valve is kept closed and the ATI is closed) where an increased pressure is detected if the valve is leaking while the pressure is kept at a constant, low pressure if the fault indicated is caused by a clogged ATI.
Even though there are certain features in the schematic table of fault indications in table 1 which seems to be not distinguishable from each other, the fault may be localized by the use of an OBD which is monitoring the overall exhaust gas purification system. For example, the symptoms that a sensor is stuck in a position indicating low pressure and the symptom that the valve is stuck in closed position (and the conduit is empty) have the same indication in table 1. Likewise, when the sensor is stuck in a position indicating high pressure and the ATI is stuck in closed position, the same pressure indications are present according to table 1. However, it will still be easy to monitor if it is the sensor or the valve/ATI which is failing by using the OBD system checking the functionality of the overall performance of the exhaust gas treatment system. If the functionality of the purification of gases still is working satisfactorily, it can unambiguously be deduced that it is the pressure sensor which is failing while if the purification of gases not is working satisfactorily, it is most probably the valve or ATI which is failing. If for example, an elevated amount of NOx is detected, it may be an indication of malfunctioning of an ATSIS for urea. If it is indicated constant high or low pressure from the pressure sensor during the test cycle, it may be deduced that the flow control (low pressure indicated) or the ATI (high pressure indicated) are stuck in closed positions. Likewise, the same distinguishing of a faulty component may be done if it is detected a relatively constant temperature of the exhaust gases downstream a filter during a regeneration cycle. Such monitoring systems, using temperature sensors, lambda sensors or the like indicating devices for monitoring the state of a system, are well known in the art and are commonly used in vehicles OBD systems. Hence, it would thus be possible to add this information together with the information from the ATSIS to be able to distinguish an error indication of the sensor from an error of the valve or ATI function.
The ATSIS monitoring system may for example only be used when there is a malfunctioning in the exhaust gas treatment system so as to deduce whether it is the ATSIS or some of the exhaust gas purification units, e.g. a filter, catalyst or trap, which is malfunctioning. A positive result from the test cycle described above would clearly indicate that the ATSIS is working as it should and it can be deduced that it is some of the other components of the system which not is working satisfactorily.
In table 1, a very simplified model for a certain test cycle is described describing very briefly the principles of how the inventive idea may be used. Preferably there is a curve made for each desired test cycle comprising the standard values for a working ATSIS. This curve may be made as a general curve according to a standard value for the system and a specific cycle. It would also be possible to log a cycle for a specific system of a specific vehicle. In this case it would be possible to adjust the curve for the natural deterioration of a system which still works well enough even though its efficiency is not as good as for a brand new system. For example, there has been an inspection including renovation and/or replacement of one or several parts of the exhaust gas treatment system including an ATSIS. When the replacement/renovation is considered done, and the system should be ready to work, a new reference curve may be logged and used as the comparative curve for this specific system. Some times this adaptation may be necessary if the system is upgraded and some essential parameters are adjusted or replacement of components demanding different operating parameters, e.g. a new ATI is mounted to the system which requires a higher delivery pressure. The above monitoring system may thus easily be modified in order to compensate for the changes introduced in the system and still work in a satisfactorily way for controlling the performance of the system.
Below follows a detailed description of a system which is adapted to involve the features of the above described method. It shall be noted that the system described herein may either be constructed as described below or used to modify an existing system, e.g. the system described in EP 1 176 292, so as to provide an improved monitoring of an after treatment substance injection system.